1. Field of the Invention
The present invention relates to a touch input system and a touch detection method using the same, by which the size and manufacturing costs of the stylus are reduced while finger touch and touch of stylus without a battery are distinguished and detected.
2. Discussion of the Related Art
With the advent of an increased information age, a display field for visually expressing electrical information signals has rapidly developed. To meet this trend, various flat display devices having excellent performance characteristics, i.e., miniaturized, lightweight, and low power consumption, have been developed.
Examples of flat display devices may include liquid crystal display devices, plasma display panel devices, field emission display devices (FEDs), organic light emitting diode display devices, etc.
In accordance with current trends, a touch panel for recognizing a touch portion via a human hand or a separate input unit and transmitting separate information corresponding to the touch has been added to a flat display device. Currently, the touch panel is added to an external surface of the display device. In addition, according to a touch detection manner, the touch panel is classified into a resistive touch panel, a capacitive panel, an infrared touch panel, etc. Recently, in consideration of convenience of a manufacturing method, detection capability, etc., capacitive panels have attracted attention.
In accordance with current trends, a smart phone, a smart book, etc. as the most compelling mobile device have used a stylus that can write or draw a picture via a pen as well as a touch input using a finger, as a human interface device (HID). Stylus input is advantageous in that more detailed input is possible than with a finger and detailed drawing and writing functions are supported.
Hereinafter, a general capacitive touch screen will be described with reference to the appended drawings.
FIG. 1 is a circuit diagram of a touch detection circuit of a general capacitive touch screen. FIG. 2 is a graph illustrating voltage output based on time according to presence of finger touch using the circuit diagram of FIG. 1.
As illustrated in FIG. 1, the touch detection circuit of the general capacitive touch screen includes a first electrode Tx and a second electrode Rx that intersect, an amplifier 5 that receives output of the second electrode Rx via a negative (−) input terminal and receives a reference voltage Vref via a positive (+) input terminal, and a capacitor Cs formed between an output terminal of the amplifier 5 and the negative (−) input terminal.
Here, the first electrode Tx receives an input voltage Vin through a pad formed at one end thereof and senses an output voltage Vout output through the amplifier 5 via a pad formed at one end of the second electrode Rx.
In general, a touch drive signal of a square wave of about 2 to 3 μs as an input voltage is applied to the first electrode Tx. In this case, a voltage proportional to mutual capacitance ΔCm between the first and second electrodes Tx and Rx is sensed as the output voltage Vout.
As illustrated in FIG. 2, when the square wave is applied as the input voltage, the output voltage Vout increases over time (when finger touch is not present). In this regard, when finger touch is present, the finger comes into contact with an electrode such that mutual capacitance variation ΔCm is reduced, and thus, an amount of increase in the output voltage Vout is reduced. The reduction amount is obtained from an intersection between a Tx channel and an Rx channel to calculate data, and coordinates of finger touch portion may be extracted from the data.
However, when the touch detection circuit of FIG. 1 is used for stylus touch instead of finger touch, since a contact area between a tip of the stylus and a sensor panel surface is relatively small, mutual capacitance variation ΔCm between electrodes is small, and thus, it is difficult to sense a change in mutual capacitance during the stylus touch. Thus, accuracy of coordinate extraction is reduced.
When the tip of the stylus is small compared with an electrode formed on the sensor panel for sensing, coordinate distortion occurs according to presence of an electrode, thereby directly affecting sensitivity.
In addition, in cases of the finger touch and the stylus touch using the same touch detection circuit, when touch is input via the stylus, problems arise in that a palm touch and the stylus touch on the electrode cannot be distinguished. That is, it is difficult to provide a palm rejection function during stylus touch to the detection circuit of FIG. 1.
Although a method of driving the stylus touch using a different method, e.g., an electromagnetic driving method from the finger touch has been introduced, in this case, a separate panel for detection via electromagnetic driving is further required in addition to the capacitive electrode, thereby increasing the number of components and manufacturing processes.